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8dab9197 | 1 | ============== |
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2 | Userspace LEDs |
3 | ============== | |
4 | ||
5 | The uleds driver supports userspace LEDs. This can be useful for testing | |
6 | triggers and can also be used to implement virtual LEDs. | |
7 | ||
8 | ||
9 | Usage | |
10 | ===== | |
11 | ||
12 | When the driver is loaded, a character device is created at /dev/uleds. To | |
13 | create a new LED class device, open /dev/uleds and write a uleds_user_dev | |
8dab9197 | 14 | structure to it (found in kernel public header file linux/uleds.h):: |
e381322b DL |
15 | |
16 | #define LED_MAX_NAME_SIZE 64 | |
17 | ||
18 | struct uleds_user_dev { | |
8dab9197 | 19 | char name[LED_MAX_NAME_SIZE]; |
e381322b DL |
20 | }; |
21 | ||
22 | A new LED class device will be created with the name given. The name can be | |
23 | any valid sysfs device node name, but consider using the LED class naming | |
24 | convention of "devicename:color:function". | |
25 | ||
26 | The current brightness is found by reading a single byte from the character | |
27 | device. Values are unsigned: 0 to 255. Reading will block until the brightness | |
28 | changes. The device node can also be polled to notify when the brightness value | |
29 | changes. | |
30 | ||
31 | The LED class device will be removed when the open file handle to /dev/uleds | |
32 | is closed. | |
33 | ||
34 | Multiple LED class devices are created by opening additional file handles to | |
35 | /dev/uleds. | |
36 | ||
37 | See tools/leds/uledmon.c for an example userspace program. |